The present invention pertains to an apparatus and method for projection exposure, which is used for a work, such as a printed circuit board, a liquid crystal board or a color filter for liquid crystal, by projecting a predetermined pattern of a mask onto the work via a projection optical system.
Many kinds of apparatus for projection exposure, which are able to conduct exposure with ultraviolet light of a predetermined wave length, have been introduced for forming a pattern such as an electric circuit for a printed circuit board, a liquid crystal board, a color filter for a liquid crystal and the like.
As shown in FIG. 14 for example, a conventional apparatus 70 for projection exposure includes a light illumination unit 71, a first reflector 72, a fly's eye lens 73, a second reflector 74, a collimating lens 75, a mask M disposed directly under the collimating lens 75, a projection lens 76, a work stage 77 and an image capturing unit 78 such as a CCD camera. A brief description is given to each of these components. The light illumination unit 71 emits light rays carrying ultraviolet light. The first reflector 72 reflects the light rays to steer the optical path of the light rays. The fly's eye lens 73 adjusts the light rays reflected by the first reflector 72. The second reflector 74 reflects the light rays coming through the fly's eye lens 73 so as to change their direction. The collimating lens 75 is disposed in the optical path of the light rays reflected by the second reflector 74. The projection lens 76 is vertically disposed right under the mask M. A work W, which is positioned right under the projection lens 76, is placed on the work stage 77. The image capturing unit 78 is disposed under the work stage 77. Japanese Published Patent Application H9-115812 discloses the related arts.
As shown in FIGS. 15A and 15B, another conventional apparatus 80 for projection exposure includes a light source 81, a reflector 82, a projection lens system 83, a roof prism 84, a right-angle prism 85, a plano-convex lens 86, and a concavo-convex lens 87, a meniscus lens 88, a reflection mirror 89 and a magnification adjuster 90. Brief description is given to each of these components. The light source 81 emits light rays carrying ultraviolet light. The reflector 82 reflects the light rays from the light source 81 to steer their direction. The projection lens system 83 is disposed right under the reflector 82. The roof prism 84 changes the direction of the light rays traveling from the projection lens system 83. The right-angle prism 85 is disposed confronting the roof prism 84 on a closer side of a work W. The plano-convex lens 86 is disposed next to both prisms 84 and 85. The concavo-convex lens 87 is disposed next to the plano-convex lens 86. The meniscus lens 88 is positioned a predetermined distance apart from the concavo-convex lens 87. The reflection mirror 89 is positioned another predetermined distance apart from the meniscus lens 88. The magnification adjuster 90 is disposed under the right-angle prism 85.
The magnification adjuster 90 includes a plano-concave lens 91, a plano-convex lens 92 which is positioned a given distance apart from the plano-concave lens 91, and an actuator 93 which controls the distance between them. Japanese Published Patent Application H8-179217 discloses the related arts.
However, the examples described above, which show conventional apparatus for projection exposure, have the following problems.
The conventional apparatus is not able to eliminate possible occasions of dust falling to a mask and a work, because they are both positioned horizontally relative to its base although a projection lens system is vertically disposed.
The projection lens system of the apparatus for projection exposure, in which convex and concave lenses are coaxially disposed as shown in Japanese Published Patent Application H9-115812, adjusts the magnification of a mask pattern for a work by controlling the distance between particular convex lenses or that between concave lenses. On the other hand, the projection lens system shown in Japanese Published Patent Application H8-179217 controls the distance between plano-convex and plano-concave lenses of the magnification adjuster which is disposed in the optical path of the projection lens system, thereby adjusting the magnification of a mask pattern for a work. These systems necessitate a separate adjustment for the whole optical system in addition to that for the magnification of the mask pattern, which brings its image on the work out of focus.
Recently, it has been requested for an apparatus for projection exposure to accommodate a work whose thickness is less than 0.5 mm. It is difficult to control the relative position of the exposure surface of the work in a vertical direction due to the thinness.
Although there are some which conduct exposure while they vertically hold a work, they cause inconvenience in conducting an alignment adjustment and exposure for the work because they do not have a mechanism which is able to adjust the geometric conditions for the exposure surface of the work.
Some apparatus, which introduces a carrying mechanism so as to automate replacement of a mask, between one in use and the other one waiting in a stock case, has adversely tended to be a large-scale complex. In the circumstances, a compact mechanism for replacement of a mask has been much in demand.
Furthermore, an apparatus for projection exposure, in which adjustment mechanisms such as a shutter and the like are separately disposed in an optical path between a light source and a work or along the optical path, inevitably has complicated structure or requires a cumbersome adjustment.